"Shadow the Hedgehog (シャドウ・ザ・ヘッジホッグ, Shadou za Hejjihoggu) is a character from the Sonic the Hedgehog series. He is an artificial life form in the design of a male, anthropomorphic hedgehog that was created around 50 years ago. He resembles Sonic in many ways, such as how his hover skates propel him at extreme speeds to rival those of Sonic; but he distinguishes himself with greater use of his signature ability to use Chaos Control with Chaos Emeralds. He is Sonic's rival and is the antithesis of Sonic himself in all aspects of his life. He has been featured in a variety of media, including his own self-titled game. Shadow is an anti-hero, and easily works together with either Sonic's group or Dr. Eggman, depending on what suits his own needs."
Source: Wikipedia, "Shadow_the_Hedgehog", available under the CC-BY-SA License.